Desalinization of aqueous solutions



United States Patent 3,414,509 DESALINIZATION OF AQUEOUS SOLUTIONS Herman S. Bloch, Skokie, Ill., assignor to Universal Oil Products Company, Des Plaines, Ill., a corporation of Delaware No Drawing. Original application June 19, 1964, Ser. No. 376,561, now Patent No. 3,351,549, dated Nov. 7, 1967. Divided and this application Aug. 29, 1967, Ser. No.

5 Claims. (Cl. 210-32 ABSTRACT OF THE DISCLOSURE RELATED APPLICATIONS The present application is a division of my copending application, Ser. No. 376,561, filed on June 19, 1964, now US. Patent No. 3,351,549 issued Nov. 7, 1967, all the teachings of which patent are incorporated herein by specific reference thereto.

APPLICABILITY OF INVENTION This invention relates to a process for separating water from an aqueous solution of a salt by removing both the negative and positive ions of the salt from the solution, in which process the feed stock is contacted with an ionretention agent containing polar radicals selected from certain ionic groups which entrap the salt ions by a retention mechanism involving mutual attraction between the oppositely charged polar groups residing respectively on the resin and in the ionized salt, the electrical charges of the polar groups in the resin in effect neutralizing the negative charge on the anion and the positive charge of the cation in the salt. More specifically, the invention concerns the composition of particular ion retention agents for use in increasing the water. content of an aqueous solution by the withdrawal and retention of the ,ionic components of a solution on the ion retention agent, to form a solution of reduced salt content as one product of the desalinization process, the salt concentration of which may be reduced substantially to nil, if desired, and by special desorption treatment of the spent, ion-retention material, a salt concentrate may be produced as either the primary or secondary product of the desalinization process.

The essentially organic compositions utilized in the present process as the ion or salt retention agents, or resins acquire a relatively more spent condition after they have absorbed a quantity of salt ions from the aqueous salt solution supplied to the process as feed stock, the quantity of salt retained by the adsorbent being dependent upon the temperature of the feed solution and the concentration of salt in solution in equilibrium with the salt adsorbed by the ion retention agent. The spent composition may thereafter be restored to its active or regenerated form by contacting the spent composition with water (referred to herein as a desorbent) in which the salt concentration is below the level at which the salt in solution is at equilibrium with the salt retained on "ice the resin during the preceding ion-retention stage of the process cycle, the absorbed salt ions in the composition tending to migrate from the spent ion retention agent into the aqueous desorbate phase. The salt concentration in the aqueous desorbent phase rises in direct proportion to the regeneration temperature and the salt content of the spent composition.

When the present ion retention agent is usedin a process which is the first stage of an integrated salt recovery process, the efiiuent desorbate stream comprises an aqueous salt concentrate from which the remaining water may be evaporated or removed by other means, if the salt in a dehydrated form is the desired end .product of the process. The recovery of a salt concentrate from the spent ion retention agent during the desorption stage of the process cycle, therefore, is in elIect a dewatering process on the feed stock solution as the first step in producing the dry or anhydrous salt by further removal of the remaining water from the desorbate concentrate. By thus increasing the concentration of salt in the saline solution as a result of the desorption of salt from the spent ion retention agent in the sequence of steps comprising the present process, a major proportion of the water present in the relatively dilute aqueous solution comprising the original feed stock is thereby eliminated prior .to the final stage of preparing the dried salt product. The present method of desalinization, therefore, reduces the quantity of water which must ultimately be evaporated from the feed stock solution to recover the solute in an anhydrous form. The process encompassed by this invention accordingly provides a means 'for effecting such initial reduction in the proportion of water in the feed stock solution more effectively and more economically than processes of the prior art, such as evaporation, ion exchange, electrophoresis and by other conventional procedures.

OBJECTS AND EMBODIMENTS In one of its embodiments, this invention relates to a process for the desalinization of an aqueous salt solution which comprises contacting said solution at a relatively low datum temperature with an ion retention agent comprising an organic composition containing acid-acting and base-acting polar groups in substantially equal number substituted on carbon atoms in the molecular structure of the composition in an arrangement of said groups which provides a succession of alternating acidic and basic substituents on the carbon atom skeleton, whereby substantially each acid-acting group is adjacent to a base-acting group to form a depolar aggregate which on contact with said solution retains the electropositive and electronegative ions of the salt in solution and forms a resulting ion retention agent at least partially spent with respect to its capacity to retain additional charged ions, and withdrawing at said datum temperature from the ion retention agent containing absorbed thereon the salt ions originally present in said solution a water product having a lower concentration of salt than said solution.

A more specific embodiment of the present invention concerns a means for restoring the activity of the ion retention agent for further use in contacting additional feed stock solution which comprises contacting the ion retention agent containing absorbed salt with water at a temperature relatively more elevated than said datum temperature and removing at said elevated temperature a desorbate efiluent of higher salt concentration than said feed stock solution from a resulting regenerated ion retention agent.

Other embodiments of the invention relating to specific ion retention agents, special conditions of temperature and salt concentrations at which the process operates and other specific aspects relating to the process and ion retention agent upon which the process is based will be referred to in greater detail in the following further description of the invention.

For example, a specific embodiment encompassed by my invention provides an organic substance having heatreversible ion retention capacity and being the polymer of an aromatic, ethylenically unsaturated amino acid in which the number of amino acid monomer units in the polymer is sufficient for said polymer to be water-insoluble, the acid-acting group of the amino acid being selected from the group consisting of carboxyl and sulfonic, and said acid-acting group being substituted on a carbon atom separated from the carbon atom bearing the amino group by not more than five intervening carbon atoms.

One of the principal and most useful applications of the present invention in the process for recovering water from an aqueous salt solution resides in the separation of substantially pure ion-free water from a feed stock salt solution for the sake of the water component itself and for this purpose the feed stock solution utilized for such water recovery is preferably a solution of minimum salt content; since the capacity of the ion retention agent and its efficiency in the desalinization process is inversely proportional to the concentration of salt in the feed stock solution, the yield of water per unit of feed stock increases in inverse proportion to the salt content of the feed stock. This adaptation of the process provides a means for producing potable water at a stage in the growth of world population when the present sources of water are rapidly becoming inadequate. New sources of supply are being actively sought throughout much of the world, not only for purposes of direct human and animal consumption to sustain life and maintain sanitary standards, but also for the irrigation of plant life and for the vast number of other uses requiring potable Water. Although sea water is readily available in virtually unlimited quantities and may be pumped inland for substantial distances to available heating facilities and to sources of electric power and other forms of energy, the recovery of potable water from sea water by presently known methods presents a formidable problem of cost because the separation of water from its saline solutions using such facilities as distillation, freezing, membrane dialysis, ion exchange, etc., involves the consumption of large quantities of heating, cooling and electrical utilities or requires such large outlays of capital for equipment that the per unit cost of potable water (containing not more than 500 ppm. by weight of solids) produced by such means from sea water generally exceeds the upper limit of acceptable cost which is generally about 40 cents per thousand gallons for drinking water purposes and about 19 cents per thousand gallons for irrigation purposes. Except for special uses of potable water which would justify a cost exceeding such limits, the foregoing conventional procedures have been generally discredited as reasonably feasible means for the production of potable water on a large scale.

On the other hand, in the aforementioned use of the present process for the production of salt concentrate from which the anhydrous salt may be recovered, for example, by further removal of the remaining water from the concentrate by distillation or by other means, the feed stock to the desalinization process is preferably as concentrated as feasibly available, and its desirability for this purpose increases as the concentration of salt in the feed solution increases or is inversely proportional to the ratio of water to salt in the solution.

The present process, utilizing the ion-retention agents of this invention, is operated on a repeating and alternating cycle of heating and cooling, comprising initially absorbing ions from the salt solution on the ion retention agent at the coolest temperature of the cycle, followed thereafter by removal or desorption of the ions from the spent retention agent at the relatively elevated temperature maintained during the regeneration phase of the cycle. The resulting, relatively large variations in temperature would norm-ally involve the expenditure of substantial quantities of heat to effect the large temperature swing between the absorption and regeneration stages of the process; however, the heat involved in effecting such temperature swing consists entirely of sensible heat and the resulting net consumption of heat for this purpose is much less than that required to provide the latent heat of vaporization or the latent heat of fusion in operating a desalinization process by either of the evaporation or freezing mechanisms involved in processes of desalinization in the prior art. Moreover, the use of the present process flow, which involves a heat exchange principle in which the heating and cooling capacity of the several process streams are alternately stored in and thereafter recovered from the resinous ion retention agent, provides an especially advantageous application of the process flow described in U.S. Patent No. 2,985,589, issued to D. B. Broughton et at., whereby a major proportion of the heating and cooling demands of the process can be recovered, thereby reducing the ultimate cost factors involved in the process to substantially nil. Through such special uses of the heat exchange capacity of one of the phases present in the process flow in the present method, the recovery of the water component and/or the recovery of the salt component of an aqueous saline solution may be accomplished with only nominal consumption of heating and other utilities.

SUMMARY OF INVENTION The desalinization of aqueous salt solutions in accordance with the process of this invention is dependent upon the effectiveness of a water-immiscible composition referred to herein as an ion retention agent, or resin, which is capable of forming an addition-type complex with the salt component of the feed stock solution. By contacting the feed stock solution with the compositions encompassed by the present invention, the salt ions in solution are retained in a separately recoverable phase, in effect extracting the latter from the feed stock solution and leaving, as the other phase, water of greatly reduced salt content. The process, accordingly, is dependent upon the capacity of the ion retention agent for retaining the salt ions in an absorbed state on or in the composition as water of reduced salt content and at the lowermost or datum temperature provided by the process is withdrawn from the spent resin as non-absorbed raffinate product. The feasibility of the present desalinization process as an economically justifiable means for producing a product of low cost is also dependent upon the ability of the composition to release its absorbed salt ions extracted from the aqueous feed stock solution, without the expenditure of large inputs of energy, or by other costly procedures for restoring the ion retention agent to its active or regenerated state. An integral phase of the over-all process is the release of the salt ions from the spent ion retention agent at conditions which disrupt ionic equilibrium between the ions present in the surrounding fluid phase and the ions already present in an absorbed state on the ion retention agent, whereby the ions present in the ion retention agent migrate from the resin to the surrounding fluid phase. Such disruption of ionic equilibrium is effected either by increasing the temperature of the surrounding fiuid phase (the aqueous desorbent) to a level more elevated with respect to the initial datum temperature, by reducing the salt content of the surrounding fluid phase below the salt concentration of the initial feed stock solution supplied to the process, or by combining both of the aforementioned means in a unitary regeneration procedure to promote the rate or the degree of salt removal from the ion retention agent by the mutually additive effect of both temperature and the disruption of ionic equilibrium. Although, presumably, the aqueous feed stock solution can be utilized as the source of water to effect desorption of the salt ions from the spent resin at a more elevated temperature than the level at which salt absorption took place, the absorbed ions are more nearly in equilibrium with the ions in the desorbent solution contacted therewith so that the resulting reduction in the rate of ion transfer from the ion retention agent into the desorbent when using the feed stock solution as the source of desorbent is lower than when using deionized water or a solution of lower salt content than the feed stock. A stepwise decrease in the salt content of the desorbent stream contacted with the spent ion retention agent, for example by first charging feed stock heated to the elevated temperature of the desorbent into the desorption zone, followed thereafter by contacting the resulting, partially regenerated ion retention agent with deionized water at the elevated desorption temperature is advantageous in that the procedure reduced the total quantity of deionized water required for the desorption or regeneration stage of the cycle.

The foregoing heat-reversible, ion-retaining properties of the present ion-retention agents enable the salt ions to be desorbed from the spent composition during the regeneration stage to thereby supply a regenerated resin for repeated use of the same composition in a cyclic flow arrangement for further removal of ions from the feed stock solution at a more downstream portion of the cycle.

The ion retention agents utilized herein to remove dissolved salts from aqueous feed stock solutions are members of a group of materials which in general are capable of forming a reversible complex with both the electronegative and the eletcropositive ions of the salt component of the solution. The designation of these compositions, which in some instances are solids and in other instances are liquids, as ion retention agents is thus an indication of their function in the present process, the agent in each case acting essentially as a means for withdrawing the salt ions from the solution and retaining the salt in the form of an addition complex with the composition in a sufficiently tenacious combination and for a sufficient length of time to permit the withdrawal of salt-depleted water from the downstream outlet of the ion retention zone. The ion retention zone of the process cycle must therefore contain sufiicient ion retention capacity in the form of the water immiscible ion retention agent to remove all of the salt ions from the feed stock solution at the feed stock flow rate and at the temperature and salt concentration at which the feed stock is supplied to the process.

The composition employed herein as the ion retention agent must also have the aforementioned property of reversibly releasing the salt from its addition complex with the composition as the temperature of the surrounding aqueous phase is increased beyond the ionic equilibrium temperature for the aqueous phase in contact with the spent composition. These properties characterize generally certain macromolecular weight solid or liquid resinous or resin-like materials which qualify as ion retention agents in the present process.

Compositions capable of acting as ion retention agents contain radicals having both base-exchange and acid-exchange activity, which, because they are spaced apart in the same molecule, act in their individual capacities as electronegative and electropositive ion traps but which because of their close proximity in the same molecule, form dipolar ionic groups or internal salts of a class referred to in the art as Zwitter ions. A common form of the acid-base or dipolar ion exchange groups are the amino acids, which structurally may be considered as the disubstituted ammonium salts of carboxylic or sulfonic acids having aliphatic, carbocyclic or heterocyclic aromatic or naphthenic structures surrounding the amino and acid groups as substituents. The essential, reactive unit present in the structure of the ion retention compositions of this invention may also be visualized as acid-base compositions of substantially isoelectric neutrality, but which, because of the intervention of at least one, up to about five carbon atoms between the carbon atoms bearing the acid and base groups respectively, do not react to form rigidly stable internal salts via neutralization of the amino groups with the carboxylic and/or sulfonic acid groups present as substituents within the compositions. As heretofore indicated, the acid portion of the dipolar ion group may be present as a carboxylic or sulfonic acid radical, the former in partially or completely hydrolyzed proteins (i.e., as a monoor polyamino acid) and the latter in certain synthetic compositions containing the sulfonic acid radical (SO H) and the amino base radical in the form of a polymeric ammonium or alkyl ammonium sulfonate composition. Thus, the dipolar ion units present in the structure of the com-positions herein utilized as ion retention agents include both the amino-carboxylic acids and the amino-sulfoni cacids as homogeneous or heterogeneous compositions.

The present compositions utilized as ion retention agents may also contain a predominance of either amino groups or acid groups in any particular structure and, therefore, are not necessarily wholly neutral and may have a pH either greater, or less than 7.0. In order to prevent internal salt formation between the amino and acid groups contained in the structure of the dipolar ion, these groups, respectively, are substituted on carbon atoms separated by one or more, up to about five, intervening carbon atoms, and more preferably separated by from one to three carbon atoms between the carbon atoms bearing the amino and acid groups, respectively.

The effective field of ion retention activity provided by the electropositive and electronegative ionic groups in the ion retention agent, thereby corresponds approximately to the field of the electropositive and electronegative ions of a molecule of ionized sodium chloride or other inorganic salt.

The present ion retention agents effect the removal of salt ions from aqueous solutions by means of a mechanism illustrated in the following equation for a resin containing an amino group and a carboxylic acid group acting on sodium chloride as an illustrative example:

where R is selected from the group consisting of hydrogen, alkyl containing from 1 to 5 carbon atoms, phenyl, benzyl, and alkyl phenyl, at least one of said R groups being hydrogen. In accordance with the mechanism of the ion retention process involved, the eletcropositive ammonium ion existing in the molecular structure of the ion retention agent exerts an attractive effect on the electronegative chloride ion of sodium chloride present in the aqueous solution; simultaneously, the electronegative carboxyl group present in the ion retention agent exerts an attractive effect on the electropositive sodium ion of the sodium chloride existing in a freely mobile form in the aqueous solution.

At the relatively low datum temperature utilized for treatment of the aqueous feed stock solution during the ion retention phase of the process, the respective positive and negative sodium and chloride ions of the salt migrate to the attracting, oppositely charged ionic groups present in the ion retention agent, both ions being loosely held within the ionic field of the firmly held positively and negatively charged acid-acting and base-acting groups comprising the ion retention agent. The mobile salt ions, however, are held in the dipolar complex only as long as the ambient temperature does not rupture the bonds between the salt ions and the antipode groups in the ion retention agent. At the elevated desorption temperatures provided in the present process the bonds existing between the oppositely charged ionic groups in the salt and in the ion retention agent are ruptured, regenerating the free electropositive ammonium radical and the electronegative carboxyl or sulfonic radical of the ion retention agent, simultaneously releasing the sodium chloride as a mobile ionic entity into the aqueous phase surrounding the ion retention agent. The proportion of regenerated to total resin, or the ratio of free carboxyl or sulfonic acid groups and amino base radicals to total carboxy plus carboxylate, sulfo plus sulfonate, and amino plus ammonium radicals increases as the temperature of the treating agent increases (depending upon the composition of the ion retention agent, the concentration of salt in solution and the identity of the salt), except that, at certain threshold temperatures, generally substantially below the boiling point of the aqueous desorbent, the treating agent is essentially wholly regenerated at any concentration of solute in the desorbent. What is true for the retention of the sodium and chloride ions of sodium chloride, which is one of the common components of sea water, is also generally true for the other metal-derived electropositive and electronegative ions of other salts, such as the electropositive calcium and magnesium ions of calcium chloride and magnesium chloride respectively, or the electropositive potassium and lithium and the electronegative sulfate ions of potassium and lithium sulfates as well as the ionic radicals of various other salts which are soluble in water.

The treating or ion retention agents which contain amino acid dipolar or Zwitter ion groups as the active ion-retentive centers present in their molecular structures, are provided by a variety of materials which may be derived from naturally-occurring sources, or prepared synthetically by polymerization of monomers containing one or more amino groups and carboxylic and/ or sulfouic acid groups per molecule. For example, both amino and carboxyl groups are present in or derived from water-insoluble proteins or proteinaceous materials, such as casein, leather, animal hair, soya bean proteins, nut proteins and the like, generally having molecular weights above 3000, up to about 75,000. Some of the preferred naturally occurring proteins and protein-conversion products are obtained by partial enzymatic or acid hydrolysis of a natural protein in the presence of a weak aqueous acid solution which reduces the molecular weight of the protein and hydrolyzes a portion of the carboxyamide linkages present in the molecular structure of the protein to the free amino acids.

In a process for treating a liquid feed stock utilizing the treating agent in solid, particle form, such as the present ion retention agent, it is, of course, a necessary requirement that the solid particle remain in the solid phase during the process and that it continue to be essentially insoluble in the aqueous phase at either the ion retention stage of the process or the desorption stage thereof. Accordingly, materials which tend to melt or which tend to dissolve in the aqueous phase at the relatively elevated desorption temperatures are preferably pretreated with a modifying agent prior to use in the process in order to convert the ion retention agent into a water-insoluble and/ or a refractory material to render the particular sub stance more useful and more suitable for the present ion retention-desorption process cycle. For this purpose, the material used as the ion retention agent, when derived from a substance of low melting point or of high water solubility is desirably pretreated prior to use with a reagent referred to herein as a modifying agent, including low molecular weight aldehydes.

Another modification of the composition and structure of the ion retention agent, particularly applied when the premodified form is a substance having a low melting point or when it is a water-soluble material, is the variation in which some of the free amino acid groups are condensed with a reactive ketone, preferably with an hydroxy ketone such as acetole (CH COCH OH), which undergoes condensation with the free amino and free acid groups to form a radical capable of chelating with the electropositive and the electronegative ions of the salt in the feed stock solution. The amino-carbonyl cross-linkage resulting from the condensation between the amino group of the ion retention agent and the carbonyl group of the modifying agent is formed via a mechanism substantially similar to the reaction represented in the following equation which illustrates the modification of an amino acid containing a carboxylic acid group using acetone as typically representing the modifying agents comprising ketones and aldehydes.

Compounds other than acetone which contain the reactive keto groups and which preferably contain not more than five carbon atoms on either side of the carbonyl radical, form the above type of reaction product with the amino acid ion retention agent, as illustrated above for acetone, including such compounds, as mesityl oxide, phorone, ditertiarybutylketone, acetylacetone, methylpropylketone, diethylketone, diacetyl benzene, diacetone alcohol, di-npropyl ketone, diisopropylketone, etc. The condensation is generally effected by heating a mixture of the reactants, that is, the ketone with the amino acid, preferably a partially acid-hydrolyzed protein, to a temperature of from about 40 C. to about 120 C. and thereafter removing the excess ketone from the condensation product, for example, by distillation or by extraction with a solvent such as water.

Synthetic, resin-like ion absorption agents having dipolar or internal salt structures are utilizable in the present desalinization process in either of two major physical forms: (1) solid, water-insoluble polymers of unsaturated monomers containing both basic amino and acidic dipolar groups; these polymers are useful in a procedure in which the liquid saline solution is contacted with a bed of solid particles of the ion retention agent or with a solution of the ion retention agent in a solvent immiscible with the aqueous feed stock solution, and (2) liquid organic compounds containing the functional amino and acid groups as substituent polar radicals, having molecular weights sufiiciently high (that is, above about 250) that the compound is substantially immiscible with the feed stock solution, either individually or in solution in a solvent itself immiscible with saline feed stock solutions. Such liquid ion retention agents or a solution of the composition in a liquid solvent are used in a process flow equivalent to a liquid-liquid extraction procedure, for example, under countercurrent flow conditions and preferably in an arrangement in which one of the phases is dispersed as liquid droplets in the other liquid phase, as shown in US. Patent No. 2,746,846 issued to G. R. Grunewald et al.

The aforementioned solid resinous polymers which may be conveniently utilized either in a particulate solid form or dissolved in a liquid solvent immiscible with the feed stock solution are prepared, for example, by the polymerization of ethylenically unsaturated amino acids. The term ethylenic unsaturation is intended to designate the presence of a mono-olefinic double bond in an aliphatic substituent present in the molecular structure of the monomer enabling the monomer to undergo interpolymerization with another ethylenically unsaturated monomer of the same or different composition and, if a solid copolymer is desired, containing in admixture therewith at least a nominal proportion (up to about 25 mole percent, and more preferably, from about 8 to about 15 mole percent) of a dienic compound such as a diolefinic hydrocarbon, to form an interpolymer or cross polymer of high molecular weight. Typical utiliza'ble unsaturated monomers which polymerize to form solid, resin-like copolymers at appropriate polymerization conditions include, for example, the following: (1) the various orth meta-, and para-vinyl-substituted aminosulfonic acid derivatives of benzene, including the various side-chain position isomers and especially and more preferably, the isomers in which the sulfonic and amino groups are substituted on carbon atoms of the ring separated by at-least one nuclear carbon atom, such as 2-amino-4-sulfostyrene, Z-amino sulfo-styrene, 2-amino-6-sulfo-styrene, 3-amino-5-sulfo-styrene, 4-amino-6-sulfo-styrene, 3- amino-6-sulfo-styrene, 3-arnino-5-sulfo-u-methyl styrene and the meta-sulfoand para-sulfo-N-vinyl-anilines and more preferably, as aforesaid, the isomers in which the sulfo group is para to the amino group. Another general group of compounds utilizable herein as the polymerizable monomers for the formation of the ion retention agents hereof are the styrene derivatives containing substituent amino and carboxyl radicals which are substituted either on the aromatic nucleus or in an alkyl sub stituent radical, including all of the various position isomers as well as the N-vinyl-aminobenzoic acids, such as 2-amino-4-carboxystyrene, B-amino-S-carboxystyrene, 2-amino-S-carboxystyrene, 4-amino-2-carboxystyrene, 4- amino-6-carboxystyrene, 3 amino--carboxystyrene, 2- amino-6-carboxystyrene, 3-(N-vinyl)-benzoic acid, 4-(N- vinyl)-benzoic acid, and especially the isomers in which the nuclear carbon atoms containing the carboxyl and amino substituents are separated by at least one intervening carbon atom, represented, for example, by 3- amino-S-carboxystyrene, and the meta and para N-vinylamino benzoic acids.

Polymers of unsaturated amino acids of the type hereinabove characterized, either individually or in admixture with other unsaturated monomers which form copolymer linages with the unsaturated amino acid monomer have a greater tendency to be water insoluble, if copolymerized with a cross-linking agent containing dior trifunctional groups, such as divinylbenzene, diethylene triamine, phthalic acid, acrylic acid, etc. The copolymerization may be effected by exposing the monomer or mixture of monomers to ultra-violet radiation with or without added peroxide, perchlorate or persulfate catalysts, such as benzoyl peroxide, acetyl peroxide, ammonium persulfate and ammonium perchloride. This method of polymerization is generally effected by mixing from 0.01 to 2 percent by weight of the polymerization catalyst or initiator with the reactive monomers in a polymerization reactor fabricated from quartz glass or other material through which ultraviolet radiation passes, while maintaining the reaction mixture at a temperature of from about 0 to about 50 C. Another suitable polymerization method for the production of hard polymers comprises mixing the desired catalyst, preferably a peroxide, with the monomers, adding from 3 to 10 volumes of an aqueous solution of a detergent, such as soap, in a shaker-type reactor and thereafter agitating the mixture at emulsifying conditions, for example, in an amulsion polymerization reactor, to form a stable emulsion of the monomers until polymerization is complete, as indicated by the separation of a semi-solid to solid curd from the emulsion. The polymerization is generally effected at a temperature of from about 10 to about 80 C., depending upon the reactivity of the monomers. When utilizing a cross-linking agent such as divinyl'benzene to copolymerize with the unsaturated amino acid for the purpose of increasing the water-insolubility of the resulting polymeric resin, the proportion of cross-linking agent in the polymerization reaction mixture is generally from 2 to about 30 percent, and more preferably, from about 5 to about percent, of the total weight of the mixture of unsaturated amino acid and cross-linking agent.

Since most of the ion retention capacity of the present resins or polymers resides in the surface of the ion retention agent (liquid droplet or solid particle) in contact with the aqueous feed stock solution, the salt ions in the aqueous phase being generally incapable of migrating more deeply into the resin structure than the acid and the amino groups on or adjacent to the surface of the particle, the capacity of a given weight of resin for ion retention is dependent upon, among other factors, the state of subdivision of the ion retention agent. The effective ion retention surface of a given weight of the ion retention agent is substantially increased by dissolving the resin or polymeric ion retention agent in a solvent for the resin or polymer, such as acetone or ethyl alcohol and coating the surfaces of a mass of solid particles of a suitable adsorbent material, such as charcoal, alumina (bauxite), sand, silica gel, or other particles of inert, water-insoluble, preferably porous, material with the resulting solution of the resin and thereafter evaporating the solvent from the particles suffused or impregnated with the solution, leaving a layer of the ion retention agent on the surfaces of the particles. The ion retention agent ultimately fabricated by impregnation of the inert support particle should preferably contain at least 3 percent by weight of the active ion retention agent.

Ano;her alternative modification of the ion retention agent utilizable in the process of the present invention, employing another variation in the method of contacting the aqueous feed stock solution with the ion retention agent, is represented by the formation of tailor-made amino acid molecules which contain large, hydrophobic hydrocarbon groups. The resulting amino acids generally exist in the form of liquids, semi-solids or solids. These ion retention agents are effective when dissolved in an inert solvent which is immiscible with the aqueous feed stock solution, or, if the product is a liquid, the ion retention agent is used directly in a liquid-liquid extraction procedure, with the aqueous feed stock as one of the liquid phases and the liquid amino acid as the other phase. Conventional countercurrent methods of contacting the aqueous feed stock solution with the ion retention agent immiscible therewith may be advantageously used to enhance the efficiency of the process.

Liquid ion absorption agents of the foregoing type for use in a process How similar to conventional solvent extrac ion procedures, in which the liquid contains the ion retention agent (either individually or dissolved in a nonaqueous, immiscible solvent), are characteristic of several distinct classes of compounds, including compounds having the structure of N-alkyl-ortho-amino-benzene sulfonic acids and compounds of similar structure in which the N-alkyl groups contain a sufficient number of carbon atoms, generally from ten to about thirty per molecule, to render the resulting compound water-insoluble, but oil soluble. Typical illustrative examples of such compounds are N-dodecylbenzyl-2-aminoethane sulfonic acid, N-octyl-cyclohexyl-Z-aminoethane sulfonic acid, N-dodecyl-N- bu yl m amino-benzene sulfonic acid, N-dodecyl-mamicobenzene sulfonic acid, 3-dodecyl-5-aminobenzoic acid, 3-amino 4 tetradecylbenzoic acid, N-dodecyl-paminobenzene sulfonic acid, etc.

These amino acids are preferably used as ion retention agents in solution in a water-insoluble oil, such as a paraffinic hydrocarbon solvent containing from 6 to about 20 carbon atoms, depending upon the temperature and pressure conditions maintained in the ion retention process, the solvent being of sufficient molecular weight and therefore having a boiling point sufficiently high to remain in liquid phase at the ion retention temperature and pressure. The salt content is extracted from the aqueous feed stock solution by contact of the feed stock with the liquid ion absorption agent at a relatively low datum temperature as herein specified and the resulting salt-rich, spent ion retention agent (the so-called extract phase of an extraction process), containing substantially all of the salt present in the feed stock solution contacted therewith, is separately contacted with water or an aqueous solution of lower salt concentration at the higher temperature referred to herein as the elevated temperature of desorption, for example in a separate contactor vessel, in a separate section of the process cycle, or in another portion of the extraction column. The ion retention and ion desorption stages are preferably effected under cyclic countercurrent and continuous operating conditions. The desorbate or extract product formed as an eflluent stream from the desorption stage of the process flow is removed for separate discharge from the process, while the raflinaie product consisting of water of reduced ion content (i.e., relative to the feed stock solution) and which may be substantially pure, ion-free water, is withdrawn as the raffinate portion of the feed stock solution from the downstream end of the ion retention zone.

The ion retention stage of the present process cycle is effected at the lowest temperature provided in the process cycle, herein referred to as the datum temperature, generally at a temperature of from to about C., or at whatever ambient temperature the feed stock solution is available for supply to the process. Thus, sea water is generally supplied or available at a temperature of from about 10 to about 30 C. at which ion absorption takes place readily and rapidly. The so-called elevated temperature of the present cycle, or the temperature level maintained during the process at which maximum desorption of salt from the spent resin takes place, is generally a temperature within the range of from about to about 100 C., and more preferably from about to about C. at atmospheric pressure, up to about C. at from 10 to 15 atmospheres pressure.

In desalinzation processes in which a liquid ion retention agent is contacted with the aqueous feed stock under liquid-liquid extraction conditions, the ion retention agent is preferably dissolved in a solvent which is immiscible with the aqueous feed stock solution in order to maximize extraction efficiency per unit weight of ion retention agent. Typical of such solvents are the hydrocarbons which are liquid at the operating temperatures employed in the present process, including such hydrocarbons as toluene, xylene, diethylbenzene, cumene, butylbenzene, tetramethylbenzene, a-myl benzene, and higher homologs of the benzene series, as well as the long chain paraflin and cycloparatfin series of compounds, such as decane, dodecane, eicosane, dodecylcyclohexane and various higher and lower homologs of the foregoing paraffin and cycloparaffin series of compounds. Mixtures of hydrocarbons may also be utilized as the normally liquid solvent for the ion retention agent, such as the kerosene, gas oil, or lubricating oil fractions of petroleum. Typical extraction solvents of the foregoing type generally contain from one percent up to about twenty percent by weight of the dissolved ion retention agent, although there is no upper or lower limit on the concentration of ion retention agent in the solvent phase, other than the requirement that the ion retention agent after forming its complex with the salt component of the feed stock solution, remains in solution in the solvent and carires the salt component with the ion retention agent into the desorption zone of the process flow.

Any apparatus and method commonly utilized for liquid-liquid solvent extraction, such as a centrifugal contactor and the procedure shown and described in United States Patent No. 2,758,783, issued to W. J. Podbielniak, the circulating disc contactor and the method accompanying the use of such device shown and described in United States Patent No. 2,729,545, issued to G. H. Reman et al., or the method of contacting and the apparatus for effecting the contact of a dispersed liquid with another, con tinuous liquid phase. immiscible with the dispersed liquid, shown and described in United States Patent No. 2,746,- 846 issued to G. R. Grunewald et al., as well as a large number of other devices commonly used in solvent extraction may be employed in the present process for the aforementioned water desalinization.

The following examples describe and illustrate several typical ion retention resins of this invention. In each instance the resin is tested for its ion retention capacity by the following procedure which, because it is uniformly applied to all samples tested, is a measure of the relative effectiveness of the ion-retention resin.

TEST METHOD The following runs describe processes for the desalinization of sea Water, the deionized product containing from 10 to about 1000 p.p.m. of dissolved solids, depending upon the particular ion retention agent utilized in the run. The sea water used as feed stock is a solution containing about 3.3% by weight of dissolved solids consisting mostly of sodium chloride, but which also contains significant proportions of other soluble salts, such as the halides, carbonates and sulfates of such metals as calcium, magnesium and potassium. The sea water is supplied to the process at a temperature of about 8 C. flowing directly at this temperature into the top of a vertical column contained in a tube of approximately 2 inches inside diameter by 3 feet in height packed with the particles of resin undergoing test. The particles of resin are supplied in a variety of sizes to observe the effect of particle size on the capacity of the resin compared on a weight for weight basis. As the sea water feed stock flows through the column of resin particles, deionized water product issues from the bottom of the ion retention column and the fiow of sea water is continued until chloride ions appear in the effluent. The capacity of the resin is determined on the basis of the quantity of sea water treated and the quantity of dissolved solids remaining in solution in the effluent raftinate. In the case of the liquid ion retention agents (liquid, that is, at the sea water inlet or datum temperature of 8 C.) a weighed quantity of the liquid ion retention agent is placed in a one liter flask and shaken with a given quantity of sea 'water. Deionized water product is decanted from the upper layer of liquid ion retention agent after settling and the procedure is thereafter repeated with the same sample of liquid ion retention agent until the organic phase becomes saturated with salt ions and fails to further remove dissolved solute from the next aliquot of sea water feed stock. Both the solid and liquid ion retention agents in their spent form are regenerated and their salt content removed to form a reactivated material by first mixing the deactivated or spent ion retention agent with sea water at 90 C. to partially remove the salt retained by the ion retention agent to an equilibrium concentration of sodium chloride in the solid and solution phases and thereafter the resulting, partially reactivated ion retention agent is further contacted with deionized water at 90 C. to remove substantially all of the remaining salt ions from the ion retention agent. The resulting reactivated ion retention agent is recycled for use in a succeeding run.

EXAMPLES The following specific ion retention agents, indicating their method of preparation and their physical properties are described as follows, and the ion retention capacity of the product is indicated in the following tabulated results.

Example I.Ion Retention Resin A A mixture of 10 molar proportion of the sodium salt of 3-carboxy-6-amino styrene (1850 parts by weight) per molar proportion of divinyl benzene (74 parts by weight) are copolymerized by the emulsion polymerization technique using benzoyl peroxide (0.96% by weight of the sodium salt or 1.78 weight proportions) as catalyst for the resulting copolymerization reaction. The carboxyl salt and the divinylbenzene monomer are initially emulsified in a rocking autoclave containing 75 volumes of an aqueous 0.5 percent solution of sodium oleate. After mixing in the autoclave for 15 minutes with the soap solution at 60 C., the monomers had formed a milky emulsion in the aqueous soap solution. The action of the autoclave was thereafter temporarily interrupted to charge the benzoyl peroxide catalyst into the emulsion, followed by continuing the rocking action of the autoclave reactor for an additional 35 minutes. During the ensuing copolymerization a mass of hard, amorphous solid particles of approximately spherical form and in a size range of from about 0.5 to about 2.5 millimeters in diameter separates from the aqueous phase in the autoclave.

The formed particles of copolymer are thereafter filtered from the aqueous phase, washed with water and heated in the presence of three volumes of distilled water toa temperature of about 100 C., followed by draining the resulting aqueous phase from the container at the boiling point of water, replacing the aqueous phase with an "additional three volumes of distilled water and again boiling the mixture of water and resin particles. After five successive treatments with boiling water in a manner similar to the above, the aqueous filtrate from the treated resin is substantially free of sodium ions and the recovered resin is packed into the ion adsorption column described above.

Example II.--Ion Retention Resin A-l Example III.-Ion Retention Resin B N-vinyl-Z-aminoethanesulfonic acid (N-vinyltaurine) is copolymerized with butadiene-1,3 in the presence of cumene hydroperoxide catalyst and ultraviolet radiation to form a solid polymer which has a melting point above the boiling point of water and is an effective ion retention agent in the process provided herein. The acidic sulfo group and the basic amino group are each substituted on one of the carbon atoms of the ethane chain and accordingly these groups are substituted on adjacent carbon atoms and there are no intervening groups between the carbon atoms bearing the base-active and acid-acting radi cals.

A mixture of 4 molar proportions of the vinyltaurine reactant per mole of butadiene is mixed at C. with 2% by weight of the mixture of reactants of a peroxide catalyst in three volume proportions based on the volume of the combined reactants in carbon bisulfide solvent. As the mixture is stirred it is exposed to ultraviolet radiation generated by a mercury vapor arc lamp suspended over the surface of the stirred reaction mixture. After 3.5 hours the copolymerization reaction mixture containing the copolymer dissolved in the carbon bisulfide solvent is poured onto ten volumes of silica gel spheres of about 0.5 mm. diameter, formed by gelling droplets of silica sol (acidified aqueous sodium silicate) suspended in an oil bath which have been subsequently dehydrated by heating to a temperature of 150 C. for six hours. The resulting silica gel particles impregnated with the carbon disulfide solution of the copolymer are washed with alcohol to remove residual peroxide catalyst and thereafter the pellets are heated in a vented oven to remove the solvent by evaporation. The resulting silica gel particles are recovered in a dry, porous form containing the ion retention agent uniformly distributed throughout the porous structure of the silica gel particles. The ion retention agent is active as an ion exchange medium only by virtue of the availability of the centers of activity on or near the surface of the resin exposed to and wetted by the saline l 4 feed stock solution; therefore, the impregnation of a mass of porous solid particles with a solution of the active ion retention agent enables the use of a relatively small quantity of the actual ion retention agent to provide a comparatively larger volume of ion retention agent distributed over the extended surface of the porous support. Because the extended composition performs substantially to the same'capacity and effectiveness as particles of the resin consisting only of resin itself, the method of compositing the resin with a support greatly enlarges the volume of ion retention capacity of a given weight of the active resinous agent.

. Example IV.Ion Retention Resin C A product containing one carbon atom between the carbon atoms bearing the acid-acting group and the carbon atom bearing the base-acting radical in the ion retention agentof this invention is formed by copolymerizing N-vi'nyl-3 amino-propane sulfonic acid with butadiene-1,3 by a procedure substantially identical to the corresponding procedure for the preparation of ion retention resin B, above, except that the reactant bearing the amino and sulfo radicals has a carbon atom skeleton corresponding to propane derivative rather than ethane. The capacity and effectiveness of resin C are tabulated in the following Table I.

0 Example V.Ion Retention Resin D In order to demonstrate further the effect of the number of carbon atoms between the carbon atoms bearing the acid-acting and base-acting radicals of the copolymer resin and demonstrating the effect by results otherwise equivalent on a comparative basis butadiene-1,3 is copolymerized with iN-vinyl-4-aminobutane sulfonic acid employing the procedure, the reactant proportions and the solvent and catalyst specified hereinabove for the preparation of ion retention resin which utilized the corresponding vinyltaurine derivative. The ion retention capacity for resin D is tabulated hereinbelow in Table I.

Example VI.-Ion Retention Resin E The product containing three carbon atoms between the carbon atoms bearing the acid-acting and base-acting groups of the resulting copolymer resin is formed by copolymerizing butadiene-l,3 with N-vinyl-S-aminopentane sulfonic acid by a procedure and utilizing the reactant proportions, catalyst and solvent hereinabove specified for the preparation of ion retention resin B, except for the substitution of the corresponding pentane derivative for the ethane monomer used for the preparation of resin B. The capacity of the resin and its effectiveness for the retention of salt ions from an aqueous saline solution are tabulated in the following Table I.

Example V'II.Ion Retention Resin F Resin F is prepared by the copolymerization of butadiene-l,4 with N-vinyl-6-aminohexane sulfonic acid which forms a copolymer resin product containing four intervening carbon atoms between the carbon atoms bearing the acid-acting group and the carbon atom bearing the base-acting group. The product and its use in the present ion retention procedure demonstrates the effect of the special relationship between the respective anion-retaining and cation-retaining radicals present within the resinous composition. The copolymerization is otherwise effected at substantially the same reaction condition, reactant proportions, solvent and catalyst as specified above for the preparation of resin B.

Example VI II.Ion Retention Resin G A C amino acid is formed by a sequence of reaction steps in which decene-l (formed by dehydrobromination of decylbromide) isinitially reacted with phosgene (carbonyl chloride) and hydrogen chloride in the presence of anhydrous zinc chloride catalyst (2% by weight of the N-decene-l) in a condensation effected in a stirred pressure autoclave at C. and at a pressure of hydrogen chloride maintained at 10 atmospheres, the resulting product consisting predominantly of l-chloroformyl-Z- chlorodecane. The chlorocarbonyl group is hydrolyzed to the corresponding sodium carboxylate radical by heating the foregoing chlorocarbonyl derivatives in an autoclave at 10 atmospheres pressure and at 130 C. with a 10% aqueous caustic solution.

The resulting sodium salt of the monochloroundecanoic acid is thereafter condensed with an equimolar proportion of 1-chloro-2-nitrobutane by mixing the undecanoic acid derivative and the chloronitrobutane with two molar proportions of finely powdered magnesium and heating the mixture in a rotating autoclave containing nitrogen at 50 atmospheres pressure, at a temperature of 80 C. as the autoclave is slowly rotated during a reaction period of approximately three hours. The product which is predominantly 3-nitro-5-carboxymethyltridecane is thereafter mixed with finely divided nickel sulfide (2% by weight of the nitro compound) in an autoclave which is thereafter charged with hydrogen to a pressure of atmospheres and heated for three hours at a temperature of 60 C. as the autoclave is slowly rotated to effect intimate mixing of nickel sulfide catalyst with the salt of the pentadecanoic acid derivative. After cooling the autoclave and recovering the organic product from the inorganic material in the autoclave by elution with 95% ethanol, the alcohol extract is evaporated to dryness and the residue consisting of the sodium salt of the aminopentadecanoic acid is heated in a pressure autoclave with slightly acidified water at 110 C. followed by extraction of the resulting C amino acid, with dodecane. The extract solution was diluted with additional dodecane to an amino acid content of 2% by weight and the resulting solution was utilized in a liquid-liquid, countercurrent, solvent extraction process to remove salt from the aqueous sea water feed stock. For this purpose the sea water is charged at the sea water supply temperature of 8 C. into the top plate of a sieve-deck extraction column of the type illustrated and described in United States Patent No. 2,746,846 issued to G. R. Grunewald et al. as the aforementioned dodecane solution of the amino acid is charged into the extraction column below the lowermost plate. The hydrocarbon phase which has the least density flows upwardly through riser conduits interconnecting the superadjacent sieve-deck plates as the sea water solution is allowed to descend in droplet form through the deck perforations from the dense liquid layer of salt solution accumulating on the top surface of each deck of the column. Spent ion retention agent containing adsorbed ionic salts is removed from the top of the column and discharged into the bottom of a second column of substantially the same design as the sieve-deck extraction column used for the ion absorption stage of the process flow (i.e., the column described in G. R. Grunewald et al. patent, cited above). Simultaneously, a portion of the deionized water product recovered as raftinate in the foregoing ion absorption stage of the process is charged at a temperature of 105 C. and at a pressure of pounds per square inch into the top plate of the second column at a volume rate of flow sufiicient to produce a brine concentrate (hereinafter referred to as the extract stream of the second column) containing 12% by weight of dissolved salts. The water desorbent stream flows downwardly through the perforated decks of the column against the rising hydrocarbon phase containing in solution the ion retention agent in which the salt ions are absorbed, the desorbent dissolving the salt ions released from the spent ion retention agent as the result of the elevated temperature of the desorbent at which temperature the salt complex formed between the positive and negative salt ions and the amino and acid groups in the ion retention agent tends to decompose and release to the water phase the free salt ions, particularly when the ion concentration in the aqueous desorbent is less than sufficient to maintain ionic equilibrium with the ion retention agent in the hydrocarbon solution. The hydrocarbon phase containing regenerated ion retention agent in solution is withdrawn from the top of the extraction column and recycled to the ion absorption column, while simultaneously a brine concentrate containing 12% by weight of dissolved salts, comprising the salts initially present in the sea water, is withdrawn from the bottom of the extraction column and discarded.

The following Table I presents the results of the foregoing treatment of sea water to remove its dissolved salt components utilizing the solid and liquid ion retention agents designated as A to G and the procedure hereinabove described for contacting the immiscible phases.

Ion Sea water treat- Residual solids Restoration of retention edion retention in desalinized mnretention agent 1 agent, decagrams/ water, p.p.m. activity after gram 2 desorption,

percent 4 1 As identified and characterized in the foregoing description.

2 As indicated by the appearance of sodium chloride in the rafiinate effluent and based on the quantity of supported material (i.e., support plus ion retention agent) present in the phase contacted with the feed stock (sea water).

3 Measure of the solids content of the last cc. of the raffinate efiluent withdrawn from the spent ion retention agent; the solids content of the first 10 cc. of rafiinate is, in each instance, nil.

4 Average of ten successive desorption-regeneration procedures on the same sample of ion retention agent.

5 Based on amino-acid.

' Average for entire efiluent.

1 Raffinate effluent constant.

I claim as my invention:

1. An organic substance having heat-reversible ion retention capacity selected from the group consisting of (1) a polymer of a monocyclic aromatic amino acid containing a nuclearly attached amino group and an ethylenically unsaturated aliphatic radical, the acid group thereof being carboxyl or sulfonic and being nuclearly attached, and (2) the copolymer of said acid with a nuclearly divinylsubstituted aromatic hydrocarbon, the number of amino acid monomer units in said substance being sufiicient for said substance to be water-insoluble.

2. The substance of claim 1 further characterized in that said aliphatic radical is a vinyl group.

3. The substance of claim 1 being the copolymer of said acid with a nuclearly divinyl-substituted aromatic hydrocarbon.

4. A process for the desalinization of an aqueous solution of a dissolved salt which comprises contacting said solution at a low datum temperature with an ion retention agent comprising the water-insoluble organic substance of claim 1, substantially each acid group of the substance adjacent to an amino group of the substance forming a di-polar aggregate which on contact with said solution withdraws the electropositive and electronegative ions of the salt from the solution and forms a resulting complex between the acid and amino groups in the ion retention agent with the electronegative and electropositive ions of said salt and withdrawing at said datum temperature from the ion retention agent containing adsorbed thereon the salt ions originally present in said solution a water product in which the concentration of salt is less than the salt concentration of said solution.

5. The process of claim 4 further characterized in that the activity of the ion retention agent for further use in contacting additional feed stock solution is restored by contacting the ion retention agent containing adsorbed thereon the salt ions withdrawn from said solution in the ion retention stage of the process with water at a temperature relatively more elevated than said datum temperature and removing at said elevated temperature a desorbate effluent of higher salt concentration than said feed stock solution from the resulting regenerated ion retention agent.

References Cited UNITED STATES PATENTS Urbain et a1. 210 37 Wilkinson. Hatch 210-38 X Hatch 210-47 x 18 OTHER REFERENCES Report No. 27, Saline Water Conversion, Advances in Chemistry Series, American "Chemical Society, Washington, DO, 1960, pp. 5053 relied on.

REUBEN FRIEDMAN, Primary Examiner.

C. DITLOW, Assistant Examiner. 

